Answer
Geometric with a common ratio of $0.4$.
Work Step by Step
Check if there is a common ratio by diving each pair of consecutive terms:
$\dfrac{4}{10}$ $=0.4$;
$\dfrac{1.6}{4}$ $=0.4$ ;
$\dfrac{0.64}{1.6}$ $=0.4$.
The ratio is constant so the sequence is geometric.
The common ratio is $0.4$.